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Message-ID: <cf901029738d3c1be033451e31c85dfe906b437b.camel@mediatek.com>
Date: Tue, 20 Aug 2024 10:53:11 +0000
From: Tze-nan Wu (吳澤南) <Tze-nan.Wu@...iatek.com>
To: "kuniyu@...zon.com" <kuniyu@...zon.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
Cheng-Jui Wang (王正睿)
<Cheng-Jui.Wang@...iatek.com>, wsd_upstream <wsd_upstream@...iatek.com>,
Bobule Chang (張弘義) <bobule.chang@...iatek.com>,
"kuba@...nel.org" <kuba@...nel.org>, "edumazet@...gle.com"
<edumazet@...gle.com>, "pabeni@...hat.com" <pabeni@...hat.com>,
"sdf@...ichev.me" <sdf@...ichev.me>,
Yanghui Li (李阳辉) <Yanghui.Li@...iatek.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "matthias.bgg@...il.com"
<matthias.bgg@...il.com>, "davem@...emloft.net" <davem@...emloft.net>,
"angelogioacchino.delregno@...labora.com"
<angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v2] net/socket: Check cgroup_bpf_enabled() only once in
do_sock_getsockopt
On Mon, 2024-08-19 at 11:18 -0700, Kuniyuki Iwashima wrote:
>
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
> From: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
> Date: Mon, 19 Aug 2024 23:56:27 +0800
> > The return value from `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` can
> change
> > between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> > `BPF_CGROUP_RUN_PROG_GETSOCKOPT`.
> >
> > If `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` changes from "false" to
> > "true" between the invocations of
> `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
> > `BPF_CGROUP_RUN_PROG_GETSOCKOPT`, `BPF_CGROUP_RUN_PROG_GETSOCKOPT`
> will
> > receive an -EFAULT from
> `__cgroup_bpf_run_filter_getsockopt(max_optlen=0)`
> > due to `get_user()` was not reached in
> `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`.
> >
> > Scenario shown as below:
> >
> > `process A` `process B`
> > ----------- ------------
> > BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN
> > enable
> CGROUP_GETSOCKOPT
> > BPF_CGROUP_RUN_PROG_GETSOCKOPT (-EFAULT)
> >
> > To prevent this, invoke `cgroup_bpf_enabled()` only once and cache
> the
> > result in a newly added local variable `enabled`.
> > Both `BPF_CGROUP_*` macros in `do_sock_getsockopt` will then check
> their
> > condition using the same `enabled` variable as the condition
> variable,
> > instead of using the return values from `cgroup_bpf_enabled` called
> by
> > themselves as the condition variable(which could yield different
> results).
> > This ensures that either both `BPF_CGROUP_*` macros pass the
> condition
> > or neither does.
> >
> > Co-developed-by: Yanghui Li <yanghui.li@...iatek.com>
> > Signed-off-by: Yanghui Li <yanghui.li@...iatek.com>
> > Co-developed-by: Cheng-Jui Wang <cheng-jui.wang@...iatek.com>
> > Signed-off-by: Cheng-Jui Wang <cheng-jui.wang@...iatek.com>
> > Signed-off-by: Tze-nan Wu <Tze-nan.Wu@...iatek.com>
> > ---
> >
> > Chagnes from v1 to v2:
> https://lore.kernel.org/all/20240819082513.27176-1-Tze-nan.Wu@mediatek.com/
> > Instead of using cgroup_lock in the fastpath, invoke
> cgroup_bpf_enabled
> > only once and cache the value in the variable `enabled`.
> `BPF_CGROUP_*`
> > macros in do_sock_getsockopt can then both check their condition
> with
> > the same variable, ensuring that either they both passing the
> condition
> > or both do not.
> >
> > Appreciate for reviewing this!
> > This patch should make cgroup_bpf_enabled() only using once,
> > but not sure if "BPF_CGROUP_*" is modifiable?(not familiar with
> code here)
> >
> > If it's not, then maybe I can come up another patch like below one:
> > +++ b/net/socket.c
> > int max_optlen __maybe_unused;
> > const struct proto_ops *ops;
> > int err;
> > + bool enabled;
> >
> > err = security_socket_getsockopt(sock, level, optname);
> > if (err)
> > return err;
> >
> > - if (!compat)
> > + enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> > + if (!compat && enabled)
> > max_optlen =
> BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> >
> > But this will cause do_sock_getsockopt calling cgroup_bpf_enabled
> up to
> > three times , Wondering which approach will be more acceptable?
> >
> > ---
> > include/linux/bpf-cgroup.h | 13 ++++++-------
> > net/socket.c | 9 ++++++---
> > 2 files changed, 12 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-
> cgroup.h
> > index fb3c3e7181e6..251632d52fa9 100644
> > --- a/include/linux/bpf-cgroup.h
> > +++ b/include/linux/bpf-cgroup.h
> > @@ -390,20 +390,19 @@ static inline bool
> cgroup_bpf_sock_enabled(struct sock *sk,
> > __ret;
> \
> > })
> >
> > -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen)
> \
> > +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled)
> \
>
> Please keep \ aligned. Same for other places.
>
>
> > ({
> \
> > int __ret = 0;
> \
> > - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))
> \
>
> Can you assign 'enabled' here to hide its usage in the macro ?
Hi Kuniyuki,
No Problem, and thanks for your recommendation.
Version 3 has hide the cgroup_bpf_enabled in macro,
and fix the coding sytle issue.
--Tze-nan
>
>
> > + if (enabled) \
> > copy_from_sockptr(&__ret, optlen, sizeof(int));
> \
> > __ret;
> \
> > })
> >
> > #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname,
> optval, optlen, \
> > - max_optlen, retval)
> \
> > + max_optlen, retval, enabled)
> \
> > ({
> \
> > int __ret = retval;
> \
> > - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) &&
> \
> > - cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))
> \
> > + if (enabled && cgroup_bpf_sock_enabled(sock,
> CGROUP_GETSOCKOPT)) \
> > if (!(sock)->sk_prot->bpf_bypass_getsockopt ||
> \
> > !INDIRECT_CALL_INET_1((sock)->sk_prot-
> >bpf_bypass_getsockopt, \
> > tcp_bpf_bypass_getsockopt,
> \
> > @@ -518,9 +517,9 @@ static inline int
> bpf_percpu_cgroup_storage_update(struct bpf_map *map,
> > #define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops) ({ 0; })
> > #define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(atype, major, minor,
> access) ({ 0; })
> > #define BPF_CGROUP_RUN_PROG_SYSCTL(head,table,write,buf,count,pos)
> ({ 0; })
> > -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) ({ 0; })
> > +#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled) ({ 0; })
> > #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname,
> optval, \
> > - optlen, max_optlen, retval) ({
> retval; })
> > + optlen, max_optlen, retval,
> enabled) ({ retval; })
> > #define BPF_CGROUP_RUN_PROG_GETSOCKOPT_KERN(sock, level, optname,
> optval, \
> > optlen, retval) ({ retval;
> })
> > #define BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock, level, optname,
> optval, optlen, \
> > diff --git a/net/socket.c b/net/socket.c
> > index fcbdd5bc47ac..5336a2755bb4 100644
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -2365,13 +2365,16 @@ int do_sock_getsockopt(struct socket *sock,
> bool compat, int level,
> > int max_optlen __maybe_unused;
> > const struct proto_ops *ops;
> > int err;
> > + bool enabled;
>
> Please keep reverse xmas tree order.
>
https://docs.kernel.org/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs
>
>
> >
> > err = security_socket_getsockopt(sock, level, optname);
> > if (err)
> > return err;
> >
> > - if (!compat)
> > - max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> > + if (!compat) {
> > + enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> > + max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen,
> enabled);
> > + }
> >
> > ops = READ_ONCE(sock->ops);
> > if (level == SOL_SOCKET) {
> > @@ -2390,7 +2393,7 @@ int do_sock_getsockopt(struct socket *sock,
> bool compat, int level,
> > if (!compat)
> > err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level,
> optname,
> > optval, optlen,
> max_optlen,
> > - err);
> > + err, enabled);
> >
> > return err;
> > }
> > --
> > 2.45.2
>
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